Please provide a concise clinical practice guideline (CPG) for adult community‑acquired pneumonia based on the latest Infectious Diseases Society of America (IDSA) and American Thoracic Society (ATS) recommendations, formatted as bullet points, an algorithm, or a flow chart.

Community-Acquired Pneumonia (CAP) Clinical Practice Guideline

Initial Assessment & Site-of-Care Decision

Use validated severity scores (PSI or CURB-65) combined with clinical judgment to determine hospitalization need. 1

Outpatient Management (PSI I-III or CURB-65 0-1)

• Treat patients with PSI class I-III as outpatients unless unstable comorbidities exist 1
• CURB-65 score ≥2 mandates hospital admission 1
• Any single major criterion (septic shock requiring vasopressors OR respiratory failure requiring mechanical ventilation) requires ICU admission 1, 2
• Presence of ≥3 minor criteria (confusion, respiratory rate ≥30/min, systolic BP <90 mmHg, multilobar infiltrates, PaO₂/FiO₂ <250) requires ICU admission 1, 2

Diagnostic Testing

For all hospitalized patients:

• Obtain chest radiography to confirm pneumonia 3
• Draw two sets of blood cultures before antibiotics 3, 1
• Collect sputum for Gram stain and culture before antibiotics 3, 1
• Measure complete blood count, serum creatinine, blood urea nitrogen, glucose, electrolytes, liver function tests 3
• Assess oxygen saturation 3
• Consider HIV serology with informed consent, especially for persons aged 15-54 years 3

For outpatients:

• Chest radiography is not strictly required for clinically stable patients but confirms diagnosis when available 1
• Routine microbiological investigations are not recommended 1

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Empiric Antibiotic Therapy

Outpatient Treatment – Previously Healthy Adults (No Comorbidities)

First-line: Amoxicillin 1 g orally three times daily for 5-7 days 1

• Retains activity against 90-95% of Streptococcus pneumoniae isolates, including many penicillin-resistant strains 1
• Provides superior pneumococcal coverage compared with oral cephalosporins 1

Alternative: Doxycycline 100 mg orally twice daily for 5-7 days 1

• Covers both typical and atypical pathogens 1

Macrolides (azithromycin or clarithromycin) should ONLY be used when local pneumococcal macrolide resistance is documented <25% 1

• In most U.S. regions, resistance is 20-30%, making macrolide monotherapy unsafe as first-line 1

Outpatient Treatment – Adults with Comorbidities

Comorbidities include: COPD, diabetes, chronic heart/liver/renal disease, malignancy, asplenia, immunosuppression, or antibiotic use within past 90 days 1

Option 1 – Combination therapy:

• β-lactam (amoxicillin-clavulanate 875/125 mg twice daily, cefpodoxime, or cefuroxime) PLUS macrolide (azithromycin or clarithromycin) OR doxycycline 100 mg twice daily 1

Option 2 – Respiratory fluoroquinolone monotherapy:

• Levofloxacin 750 mg daily OR moxifloxacin 400 mg daily for 5-7 days 1
• Reserve for patients with β-lactam allergy or contraindications to macrolides due to FDA safety warnings 1

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Hospitalized Patients (Non-ICU)

Two equally effective regimens with strong evidence: 1

Preferred Regimen:

Ceftriaxone 1-2 g IV once daily PLUS azithromycin 500 mg IV or orally daily 1

• Covers typical pathogens (S. pneumoniae, H. influenzae, M. catarrhalis) and atypical organisms (Mycoplasma, Chlamydophila, Legionella) 1
• Alternative β-lactams: cefotaxime 1-2 g IV every 8 hours OR ampicillin-sulbactam 3 g IV every 6 hours, always combined with macrolide 1

Alternative Regimen:

Respiratory fluoroquinolone monotherapy: levofloxacin 750 mg IV daily OR moxifloxacin 400 mg IV daily 1

• Preferred for penicillin-allergic patients 1

Critical timing: Administer first antibiotic dose in the emergency department immediately upon diagnosis 1

• Delays beyond 8 hours increase 30-day mortality by 20-30% 1

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Severe CAP Requiring ICU Admission

Combination therapy is MANDATORY for all ICU patients – β-lactam monotherapy is associated with higher mortality 1, 2

Preferred ICU Regimen:

Ceftriaxone 2 g IV once daily (or cefotaxime 1-2 g IV every 8 hours or ampicillin-sulbactam 3 g IV every 6 hours) PLUS azithromycin 500 mg IV daily OR respiratory fluoroquinolone (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily) 1, 2

For Penicillin-Allergic ICU Patients:

Aztreonam 2 g IV every 8 hours PLUS respiratory fluoroquinolone 1

Adjunctive ICU Therapies:

• Screen hypotensive, fluid-resuscitated patients for occult adrenal insufficiency 2
• Provide cautious trial of noninvasive ventilation for hypoxemia unless immediate intubation required 2
• Use low-tidal-volume ventilation (6 mL/kg ideal body weight) for diffuse bilateral pneumonia or ARDS 2

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Special Pathogen Coverage (Add ONLY When Risk Factors Present)

Pseudomonas aeruginosa Coverage

Add antipseudomonal therapy ONLY if patient has: 1

• Structural lung disease (bronchiectasis, cystic fibrosis)
• Recent hospitalization with IV antibiotics within 90 days
• Prior respiratory isolation of P. aeruginosa
• Chronic broad-spectrum antibiotic exposure (≥7 days in past month)

Regimen: Antipseudomonal β-lactam (piperacillin-tazobactam 4.5 g IV every 6 hours OR cefepime 2 g IV every 8 hours OR carbapenem) PLUS ciprofloxacin 400 mg IV every 8 hours OR levofloxacin 750 mg IV daily PLUS aminoglycoside (gentamicin or tobramycin 5-7 mg/kg IV daily) 1

MRSA Coverage

Add MRSA therapy ONLY if patient has: 1

• Prior MRSA infection or colonization
• Recent hospitalization with IV antibiotics
• Post-influenza pneumonia
• Cavitary infiltrates on imaging

Regimen: Vancomycin 15 mg/kg IV every 8-12 hours (target trough 15-20 µg/mL) OR linezolid 600 mg IV every 12 hours, added to base CAP regimen 1

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Duration of Therapy & Transition to Oral Antibiotics

Minimum Duration:

Treat for minimum of 5 days AND continue until patient is afebrile for 48-72 hours with no more than one sign of clinical instability 1, 2

Typical Duration:

• Uncomplicated CAP: 5-7 days total 1, 2
• Extended duration (14-21 days) ONLY for: Legionella pneumophila, Staphylococcus aureus, or Gram-negative enteric bacilli 1, 2

Transition to Oral Therapy:

Switch from IV to oral when ALL stability criteria met (typically hospital day 2-3): 1, 2

• Temperature ≤37.8°C
• Heart rate ≤100 bpm
• Respiratory rate ≤24 breaths/min
• Systolic BP ≥90 mmHg
• Oxygen saturation ≥90% on room air
• Able to maintain oral intake
• Normal mental status

Oral step-down options:

• Amoxicillin 1 g three times daily PLUS azithromycin 500 mg daily 1
• Continue azithromycin alone after 2-3 days of IV therapy 1

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Monitoring & Management of Treatment Failure

Inpatient Monitoring:

Monitor temperature, respiratory rate, pulse, blood pressure, mental status, and oxygen saturation at least twice daily 1, 2

If No Clinical Improvement by Day 2-3:

Obtain: 1, 2

• Repeat chest radiograph
• Inflammatory markers (CRP, white blood cell count)
• Additional microbiologic specimens
• Consider chest CT to evaluate for complications (pleural effusion, empyema, lung abscess)

Escalation Strategies:

• For non-severe pneumonia on amoxicillin monotherapy: Add or substitute macrolide 1, 2
• For non-severe pneumonia on combination therapy: Switch to respiratory fluoroquinolone 1, 2
• For severe pneumonia not responding: Consider adding rifampicin 2

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Follow-Up

Outpatient Follow-Up:

Clinical review at 48 hours (or sooner if symptoms worsen) 1

• Assess symptom resolution, oral intake, treatment response

All Patients:

Routine follow-up at 6 weeks 1

• Chest radiograph ONLY if symptoms persist, physical signs remain, or high risk for underlying malignancy (smokers >50 years) 1

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Prevention

Pneumococcal vaccination: 1

• All adults ≥65 years
• Adults with high-risk conditions (chronic heart/lung/liver disease, diabetes, immunosuppression)

Annual influenza vaccination for all patients 1

Smoking cessation counseling for all current smokers 1

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Critical Pitfalls to Avoid

Never use macrolide monotherapy in hospitalized patients – fails to cover typical pathogens like S. pneumoniae 1

Never use macrolide monotherapy in areas where pneumococcal macrolide resistance exceeds 25% – leads to treatment failure 1

Never delay antibiotic administration beyond 8 hours – increases 30-day mortality by 20-30% 1

Never add broad-spectrum antipseudomonal or MRSA agents without documented risk factors – promotes resistance without benefit 1

Never use β-lactam monotherapy in ICU patients – associated with higher mortality 1, 2

Always obtain blood and sputum cultures before starting antibiotics in hospitalized patients – enables pathogen-directed therapy 1

Never extend therapy beyond 7-8 days in responding patients without specific indications – increases resistance risk 1